1. Field of the Invention
The present invention relates to apparatus for controlling remotely an electrically controlled device such as a dictating machine, and more particularly to such apparatus which is controllable by means of a telephone instrument over a telephone transmission line.
2. Prior Art
It is frequently desirable to remotely control apparatus such as a dictating machine or the like using an ordinary telephone line, with control signals originated by operation of a conventional telephone instrument, sometimes referred to herein as a telephone handset. Several attempts at accomplishing this have been made in the past, but such attempts have not met with unqualified success for a variety of reasons. In the first place, much of the apparatus heretofore known does not permit use of the dictating machine equipment remotely with the same facility and with the same full range of operating functions as are available when such equipment is operated manually by the operator in person, and is not suitable for use with a variety of different types or styles of dictating machines. Moreover, the apparatus of the prior art has not provided means for controlling the dictation machine entirely through the microphone cable jack or plug, but additional wiring changes within the dictating machine have also been necessary.
Further, such systems have heretofore been usable only with certain kinds of transmission lines and with certain kinds of handsets. This has limited the apparatus to use only under relatively restricted conditions, such as, for example, where the parameters of the transmission line are known with some precision, as are the amplitudes of the control signals, etc. These restrictions effectively prevent operation of the equipment via any telephone transmission line, such as long distance lines, etc., where the parameters cannot be known with precision because of variations from line to line.
The previously known systems have also not had a capability to operate in response to operation of either a coded tone handset or a dial type handset, and they are subject to faulty operation because of the vast difference between the level of control signals and sigals to be recorded, and the level of signals being played back.
The systems of the prior art have also been subject to faulty operation in response to spurious signals present on the transmission line, and do not adequately operate to release the transmission line in response to the presence of a dial tone on it.